In this context, the filter with system function represented by Eq. (103) is called an interpolated FIR filter. This is because the corresponding impulse response can be seen to be the convolution of $h_1[n]$ with the second impulse response expanded by $M_1$.
- This explanation as to why Eq. (103) is called an interpolated FIR filter is still not clear for me.
- Why is the impulse response given by Eq (104) FIR?